1. Field of the Invention
The present invention relates to a coating method for coating a sheet-shaped or web-shaped base material (hereinafter referred to as a xe2x80x9cwebxe2x80x9d) such as a metal sheet, paper and film with a variety of liquid substances (hereinafter referred to as xe2x80x9ccoating liquidsxe2x80x9d).
2. Description of Related Art
A variety of coating apparatuses such as a roll coater, an air knife coater, a coater using a die and a rod coater are known that coat a web such as a metal sheet, paper and plastic film with a variety of coating liquids.
Among these coating apparatuses, the rod coater is widely used since it is simple and is capable of coating a variety of webs with a variety of coating liquids. There are two types of rod coaters. One removes, by means of a coating rod, a surplus of the coating liquid that has been applied on the web, and the other applies the coating liquid on the web and adjusts the amount of the coating liquid by one coating rod. In both types of the rod coaters, a number of grooves are formed on the surface of the coating rod along the circumferential direction. The amount of the coating liquid to be applied on the web and the amount of the coating liquid to be removed from the web are adjusted with the depth, width, etc. of the grooves.
In a conventional rod coater disclosed in Japanese Patent Publication No. 58-4589, the coating rod is rotated in the same direction or in the reverse direction with respect to a running direction of the continuously-running web, and the coating rod picks up the coating liquid from a pool to thereby apply the coating liquid on the web to form a coating layer on the web. In the applying, the amount of the coating liquid is measured in an area where the web becomes into contact with the rod so that only a desired amount of the coating liquid can remain on the web. The surplus of the coating liquid flows down to rejoin the pool, to which a new coating liquid is also supplied.
In the conventional coating method of Japanese Patent Publication No. 58-4589, however, xe2x80x9cstreaks at a constant pitchxe2x80x9d are formed on the surface of the coating layer on the web if a high-speed coating is performed by raising the running speed of the web or if a coating liquid with a high viscosity is applied on the web.
To prevent the formation of the xe2x80x9cstreaks at a constant pitchxe2x80x9d, it is more preferable to rotate the coating rod in the reverse direction with respect to the running direction of the web than in the same direction. Only the reverse rotation, however, cannot completely solve the problem since xe2x80x9cstreaks at a constant pitchxe2x80x9d of a different kind from the above-mentioned xe2x80x9cstreaks at a constant pitchxe2x80x9d are formed.
It is therefore an object of the present invention to provide a coating method that enables a satisfactory coating without forming the streaks if the high-speed coating is performed by raising the running speed of the web or if the web is coated with the coating liquid with a high viscosity.
The above object can be accomplished by providing a coating method for coating a continuously-running web with a coating liquid, the method comprising the steps of: applying a plenty of the coating liquid on the web to form a coating layer on the web; and removing a surplus of the coating liquid from the coating layer with a rod, the rod being in contact with the coating layer and being rotated in a reverse direction with respect to a running direction of the web, wherein an absolute value of V1/V2 is set between 0.0001 and 0.06, where V1 (cm/sec) is a rotating speed of the rod and V2 (cm/sec) is a running speed of the web.
According to the present invention, in the coating method using the coating rod, the coating is performed by rotating the coating rod in the reverse direction with respect to the running direction of the web, and setting the absolute value of V1/V2 between 0.0001 and 0.06. This prevents the formation of the streaks even if the high-speed coating is performed by raising the running speed of the web or if the coating liquid with a high viscosity is applied on the web. This enables the satisfactory coating at a low speed and a high speed.